KVM: arm/arm64: vgic: Fix GICC_PMR uaccess on GICv3 and clarify ABI
As an oversight, for GICv2, we accidentally export the GICC_PMR register
in the format of the GICH_VMCR.VMPriMask field in the lower 5 bits of a
word, meaning that userspace must always use the lower 5 bits to
communicate with the KVM device and must shift the value left by 3
places to obtain the actual priority mask level.
Since GICv3 supports the full 8 bits of priority masking in the ICH_VMCR,
we have to fix the value we export when emulating a GICv2 on top of a
hardware GICv3 and exporting the emulated GICv2 state to userspace.
Take the chance to clarify this aspect of the ABI.
Reviewed-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <cdall@linaro.org>
diff --git a/virt/kvm/arm/vgic/vgic-mmio-v2.c b/virt/kvm/arm/vgic/vgic-mmio-v2.c
index a3ad7ff..0a4283e 100644
--- a/virt/kvm/arm/vgic/vgic-mmio-v2.c
+++ b/virt/kvm/arm/vgic/vgic-mmio-v2.c
@@ -229,7 +229,15 @@
val = vmcr.ctlr;
break;
case GIC_CPU_PRIMASK:
- val = vmcr.pmr;
+ /*
+ * Our KVM_DEV_TYPE_ARM_VGIC_V2 device ABI exports the
+ * the PMR field as GICH_VMCR.VMPriMask rather than
+ * GICC_PMR.Priority, so we expose the upper five bits of
+ * priority mask to userspace using the lower bits in the
+ * unsigned long.
+ */
+ val = (vmcr.pmr & GICV_PMR_PRIORITY_MASK) >>
+ GICV_PMR_PRIORITY_SHIFT;
break;
case GIC_CPU_BINPOINT:
val = vmcr.bpr;
@@ -262,7 +270,15 @@
vmcr.ctlr = val;
break;
case GIC_CPU_PRIMASK:
- vmcr.pmr = val;
+ /*
+ * Our KVM_DEV_TYPE_ARM_VGIC_V2 device ABI exports the
+ * the PMR field as GICH_VMCR.VMPriMask rather than
+ * GICC_PMR.Priority, so we expose the upper five bits of
+ * priority mask to userspace using the lower bits in the
+ * unsigned long.
+ */
+ vmcr.pmr = (val << GICV_PMR_PRIORITY_SHIFT) &
+ GICV_PMR_PRIORITY_MASK;
break;
case GIC_CPU_BINPOINT:
vmcr.bpr = val;